Multi-sectional composite tooling

ABSTRACT

A multi-sectional composite tooling for use in molding large composite structures. The tooling includes at least two tooling sections that are made from quasi-isotropic sheet molding compound. The two tooling sections are seamed together with a scarf plug at the tooling surface. The scarf plug is composed of specially oriented layers of consolidated quasi-isotropic sheet molding compound. The scarf plug is made from the same type of quasi-isotropic sheet molding compound that is used to make the tooling sections.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to apparatus and methods used tomold composite materials into large composite structures. Moreparticularly, the present invention is directed to the multi-sectionaltools that are used to form such large composite structures and the waysin which the sections of such tools are joined together.

2. Description of Related Art

Many processes for making composite structures utilize a mold to providedesired surface contours and shapes. The mold is particularly importantin autoclave processes where the uncured resin/fiber material is heatedin the mold, under vacuum, to relatively high cure temperatures (175° C.and above) to form the final composite part or structure.

Molds made from steel alloys, such as INVAR36, are commonly used becausethey are extremely strong and can easily withstand the elevated curetemperatures used in autoclaves for composite material curing. Thesemolds are also commonly referred to as “tools” or “tooling”. Steel alloytooling can be machined to obtain tight surface profile tolerances. Inaddition, tooling for molding large structures can be made by joiningsections of steel alloy tooling together and welding the seams. Thewelded seams can be machined and polished to eliminate any imperfectionsin the mold surface to produce a seamless tooling surface that is freefrom unwanted “mark off” on the parts cured surface. Although steelalloys are well suited for making multi-sectional large tooling, thereare a number of drawbacks. For example, steel alloy tooling tends to beheavy and expensive. In addition, the time required to heat and thencool a massive multi-sectional steel alloy tooling increases the cycletime during molding of composite structures.

Tooling made from composite materials have been developed as analternative to steel alloy tooling for use in autoclave molding ofcomposite parts. Composite tooling has been popular because it istypically lighter than steel alloy tooling. The composite tooling isgenerally formed using a highly accurate master mold that is made from asteel alloy or other suitable material.

Pre-impregnated composite material (prepreg) is typically used to makecomposite tooling. Prepreg is a combination of uncured resin matrix andfiber reinforcement that is ready for molding and curing to form thecomposite tool. By pre-impregnating the fiber reinforcement with resin,the manufacturer can carefully control the amount and location of resinthat is impregnated into the fiber network and ensure that the resin isdistributed in the network as desired.

Unidirectional (UD) tape is a common form of prepreg. The fibers inunidirectional tape are continuous fibers that extend parallel to eachother. The fibers are typically in the form of bundles of numerousindividual fibers or filaments that are referred to as a “tows”. Theunidirectional fibers are impregnated with a carefully controlled amountof uncured resin. The UD prepreg is typically placed between protectivelayers to form a UD tape that is rolled up for storage or transport tothe manufacturing facility. The width of UD tape typically ranges fromless 2 cm to 30 cm or more.

Unidirectional tape is not well-suited for use in making compositetooling. The parallel orientation and continuous nature of the fibers inthe UD tape cause fiber bunching or bridging when the UD tape is forcedto fit the features of a complex tool shape. In addition, compositetooling made from UD tape cannot be machined to obtain the tight surfaceprofile tolerances that are required for composite tooling withoutsignificant tool movement.

Molding compounds, which are generically referred to as discontinuousfiber composite (DFC) molding compound, have been found to be suitablefor use in making composite tooling. One type of DFC molding compound,which is referred to herein as quasi-isotropic sheet molding compound,combines the attributes of UD tape and randomly oriented short fibersinto a single molding compound that can be accurately molded andmachined to form composite tooling. Quasi-isotropic sheet moldingcompound is composed of randomly oriented segments or chips ofunidirectional tape that have been impregnated with thermosetting resin.Quasi-isotropic sheet molding compound has been widely used to makecomposite tooling. Quasi-isotropic sheet molding compound is availablefrom Hexcel Corporation (Dublin, Calif.) under the trade names HexTool®and HexMC®. Examples of composite molds or tooling that have been madeusing HexTool® or HexMC® are described in U.S. Pat. No. 8,257,631, thecontents of which are hereby incorporated by reference.

Quasi-isotropic sheet molding compound is typically made by layingmultifilamentary tows (yams) parallel to each other on a suitablebacking and impregnating the parallel tows with resin to form a UDprepreg. The UD prepreg is then chopped to form UD chips which aregenerally from 5 mm to 25 mm wide and from 25 mm to 125 mm long. A layerof quasi-isotropically oriented UD chips is then formed. Multiple layersof the quasi-isotropically oriented UD chips are combined together toform a ply-like molding material which is used to make compositetooling.

The light weight and high strength of composite tooling makes itparticularly attractive for use in making large composite structures orparts, such as aircraft wings, aircraft fuselages, horizontal stabilizerspar tools, wing spar tools and empennage tools. Molding of such largecomposite structures requires composite tooling having surfaces that aretypically over 3 meters long and over 1 meter wide. The location wherethe composite tooling is made is usually not the same as the locationwhere the tooling is used to mold the large composite structures. It isnot practical to make a single large composite tooling at one locationand then transport it to another location for use in molding largecomposite structures. Instead, multiple tooling sections are made thatcan be transported by truck or other suitable transport to themanufacturing site where the large composite structures are molded. Onceat the manufacturing site, the multiple tool sections are joinedtogether to form the desired single large composite tooling.

An important consideration when joining multiple composite toolingsections together is ensuring that the seams between the toolingsections are filled or otherwise treated to eliminate any surfaceimperfections in the overall tooling surface. The material used to fillthe seam must be durable enough to withstand numerous molding cycles.The material used to fill the seam should also have physical properties,such as a coefficient of thermal expansion, that match the physicalproperties of the material used to make the tooling sections in order toprevent separation at the bond lines between the seam and the toolingsections. The seam filling material must be amenable to machining in thesame manner as the surfaces of the composite tooling sections in orderto provide a tooling surface that is free of imperfections at the seams.In addition, the seam filling cannot be porous or have otherimperfections which would be exposed during initial or subsequentmachining and/or polishing of the tooling surface.

SUMMARY OF THE INVENTION

In accordance with the present invention, a multi-sectional tooling isprovided in which the seams between the tooling section surfaces arefilled with a scarf plug that is made from the same type ofquasi-isotropic sheet molding compound that is used to make the toolingsections. The scarf plug is specifically designed and oriented toeliminate any surface imperfections in the overall tooling surface. Thescarf plug has the same durability as the tooling sections so that itcan withstand numerous molding cycles. In addition, the scarf plug canbe machined in the same manner as the surfaces of the composite toolingsections to provide a seamless multi-sectional tooling surface.

The multi-sectional tooling of the present invention is designed for usein molding large composite structures that have a molded surface. Themulti-sectional tooling includes a first tooling section having a firsttooling surface which is shaped to form a first portion of the moldedsurface of the large composite structure. The first tooling sectionincludes a first side surface and a first scarf surface that extends atan angle from the first tooling surface to the first side surface. Thefirst scarf surface has a first exterior edge located at the first toolsurface and a first interior edge located at the first side surface. Thefirst tooling section is made from multiple layers of curedquasi-isotropic sheet molding compound.

The multi-sectional tooling also includes a second tooling sectionhaving a second tooling surface which is shaped to form a second portionof the molded surface of the large composite structure. The secondtooling section includes a second side surface and a second scarfsurface that extends at an angle from the second tooling surface to thesecond side surface. The second scarf surface has a second exterior edgelocated at the second tooling surface and a second interior edge locatedat said second side surface. The second tooling section is also madefrom multiple layers of cured quasi-isotropic sheet molding compound.

The first tooling section and second tooling section are locatedadjacent to each other so that the first scarf surface and said secondscarf surface form a scarf seam. The scarf seam has an apex extendingalong the first and second interior edges of the scarf surfaces. Thescarf seam also has an exterior boundary extending between the first andsecond exterior edges of the scarf surfaces. The exterior boundary ofthe scarf seam is coincident with the tooling seam surface that extendsbetween the first tooling surface and second tooling surface.

As a feature of the present invention, a scarf plug is provided thatfills the scarf seam. The scarf plug includes a first scarf plug layerwhich is a layer of cured quasi-isotropic sheet molding compound thathas an interior side and an exterior side. The interior side of thefirst scarf plug layer is located adjacent to the first and second scarfsurfaces and extends from the first exterior edge located on first scarfsurface to the seam apex and from the seam apex to the second exterioredge located on the second scarf surface. The exterior side of the firstscarf plug layer has a surface contour in the shape of a chevronextending from the first exterior edge to the second exterior edge ofthe scarf seam. The scarf plug also includes a plurality of additionalscarf plug layers that are located between the exterior side of thefirst scarf plug layer and the exterior boundary of the scarf seam. Eachof the additional scarf plug layers is composed of a layer of curedquasi-isotropic sheet molding compound. Each of the additional scarfplug layers has an interior side and an exterior side. The additionalscarf plug layers are located in the scarf plug such that the interiorside of each additional scarf plug layer is located next to the exteriorside of an adjacent additional scarf plug layer that is closer to thefirst scarf plug layer. The interior side of one of the additional scarfplug layers is located next to the exterior side of the first scarf pluglayer and follows the surface contour of the first scarf plug layer. Theadditional scarf plug layers form the tooling seam surface.

As a feature of the invention, a consolidated scarf plug is preparedwhich has the shape of the desired scarf plug, but which includesuncured quasi-isotropic sheet molding compound. The consolidated scarfplugs are oversized so that a portion of the consolidated scarf plugextends above the tooling seam surface when the consolidated scarf plugis inserted into the scarf seam. After curing, the portion of the scarfplug that remains above the tooling seam surface is machined off inorder to provide a final scarf plug which has an exterior boundary thatis coincident with the tooling seam surface.

In addition to covering multi-sectional tooling and the consolidatedscarf plugs that are used to fill the seams in the tooling surface, thepresent invention also covers methods for filling the seams ofmulti-sectional tooling using the consolidated scarf plugs.

The scarf plugs in accordance with the present invention areparticularly well suited for filling the surface seams between compositetooling sections made from quasi-isotropic sheet molding compound. Thescarf plugs are durable enough to withstand numerous molding cycles inthe same manner as the tooling sections. The scarf plugs have physicalproperties, such as a coefficient of thermal expansion, that match thephysical properties of the material used to make the tooling section inorder to prevent separation at the bond lines between the seam toolingsections. The scarf plugs can be machined and/or polished in the samemanner as the surfaces of the composite tooling sections in order toprovide a tooling surface that is free of imperfections at the seams.

The process of consolidating multiple layers of quasi-isotropic sheetmolding compound to form a consolidated scarf plug, which is thenautoclave cured in the seam between the tooling sections, produces amulti-sectional tooling surface that is essentially seamless. The scarfplug seams made in this manner are not porous and they do not have otherimperfections that could be exposed during initial or subsequentmachining and/or polishing of the scarf plug and surrounding toolingsurfaces.

The above discussed and many other features and attendant advantages ofthe present invention will become better understood by reference to thedetailed description when taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial view of an exemplary multi-sectional compositetooling in accordance with the present invention showing the seambetween two tooling sections.

FIG. 2 is a side view of FIG. 1 showing details of the scarf pluglaminate structure.

FIG. 3 is a side view showing an oversized scarf plug prior to machiningto form the final scarf plug seam as shown in FIGS. 1 and 2.

FIG. 4 is a partial view of a consolidated scarf plug before it isapplied to the scarf seam.

FIG. 5 is a partial view of an exemplary three piece multi-sectionalcomposite tooling in accordance with the present invention.

FIG. 6 is a cross-sectional photograph of a scarf plug seam having a 45degree chevron cross-sectional shape.

FIG. 7 is a cross-sectional photograph of a preferred scarf plug seamhaving a 30 degree chevron cross-sectional shape.

FIG. 8 shows a simplified compression mold apparatus that is used tomake the consolidated scarf plug.

FIG. 9 is a cross-sectional view of the compression mold that is shownin FIG. 8.

DETAILED DESCRIPTION OF THE INVENTION

A portion of an exemplary multi-sectional composite tooling inaccordance with the present invention is shown at 10 in FIGS. 1 and 2.The multi-sectional tooling is intended for use in fabricating largecomposite parts or structures in accordance with known autoclave curingprocesses where service temperatures are typically between 170° C. and260° C. and where the tooling surfaces are exposed to pressures ofbetween 45 psi and 125 psi. However, if desired, the tooling may be usedin other molding processes where it is not necessary to heat thematerial being molded to such high temperatures and/or where highpressure is not used in the molding process.

Exemplary large composite parts or structures that can be molded usingthe multi-sectional tooling includes aircraft wings, fuselages,horizontal stabilizer spar tools, wing spar tools and empennage tools.The overall size of the molding surface provided by the multi-sectionaltooling can range from a few square meters to over 100 square meters.The size of the molding surface is only limited by the number of toolingsections that are joined together and the ability to properly supportthe tooling. Each section of the tooling is preferably sized so that itcan be transported by road, railway and/or air transport. Preferably,the individual tooling sections will not exceed 3 meters in width and 12meters in length.

Although the multi-sectional tooling may include any number of toolingsections, which depends upon the size of the desired over all toolingand the size of the individual sections, for exemplary purposes themulti-sectional tooling 10 is shown having only a first tooling section12 and a second tooling section 14. The tooling sections 12 and 14 aresecurely joined together by a structural joint element 17. The jointelement 17 is sufficiently strong to keep the tooling sections preciselypositioned during numerous autoclave molding cycles. The overallmulti-sectional tooling 10 is also supported by other support structures(not shown) in accordance with known molding processes that utilizecomposite tooling.

The first tooling section 12 has a first tool surface 16 which is shapedto form a first portion of the molded surface of a large compositestructure. The first tooling section 12 also includes a first sidesurface 18 and a first scarf surface 20 that extends at an angle fromthe first tool surface 16 down to the first side surface 18. The firstscarf surface 20 has a first exterior edge 22 located at the first toolsurface 16 and a first interior edge 24 located at the first sidesurface 18. The first tool section 12 is made from multiple layers ofcured quasi- isotropic sheet molding compound, such as HexTool® orHexMC®, which is composed of a plurality of randomly oriented chipswhere each chip contains unidirectionally oriented fibers and a curedresin.

The second tooling section 14 has a second tool surface 26 which isshaped to form a second portion of the molded surface of a largecomposite structure. The second tooling section 14 also includes asecond side surface 28 and a second scarf surface 30 that extends at anangle from the second tool surface 26 down to the second side surface28. The second scarf surface 30 has a second exterior edge 32 located atthe second tool surface 26 and a second interior edge 34 located at thesecond side surface 28. The second tool section 14 is made from multiplelayers of cured quasi-isotropic sheet molding compound, such as HexTool®or HexMC®, which is composed of a plurality of randomly oriented chipswhere each chip contains unidirectionally oriented fibers and a curedresin.

The first tooling section 12 and second tooling section 14 are locatedadjacent to each other so that the first scarf surface 20 and secondscarf surface 30 form a scarf seam 36 located at the surface between thetwo tooling section. The scarf seam 36 has an apex 38 that extends alongthe first interior edge 24 and second interior edge 34. The scarf seam36 also has an exterior boundary 40 that extends between the first andsecond exterior edges 22 and 32 of the tooling sections. The exteriorboundary 40 is coincident with the tooling seam surface that extendsbetween the first and second surfaces 16 and 26 of the tooling sections.

In accordance with the present invention, a scarf plug 42 fills thescarf seam 36. The scarf plug 42 includes a first scarf plug layer 44that is composed of a layer of cured quasi-isotropic sheet moldingcompound, such as HexTool® or HexMC®, which is made up of a plurality ofrandomly oriented chips where each chip contains unidirectionallyoriented fibers and a cured resin. The first scarf plug layer 44includes an interior side 46 and an exterior side 48. The interior side46 of the scarf plug is located adjacent to the first and second scarfsurfaces 20 and 30. The interior side 46 of the scarf plug layer extendsfrom the first exterior edge 22 of the first tooling to the apex 38 andfrom the apex 38 to the second exterior edge 32 of the second tooling.The exterior side 48 of the first scarf plug layer has a surface contourin the shape of a chevron that extends from the first exterior edge 22to the second exterior edge 32.

The scarf plug 42 includes a plurality of additional scarf plug layers50 a-50 i that are located between the exterior side 48 of the firstscarf plug layer and the exterior boundary 40 of the scarf seam. Each ofthe additional scarf layers 50 a-50 i is made from a layer of curedquasi-isotropic sheet molding compound, such as HexTool® or HexMC®,which is composed of a plurality of randomly oriented chips where eachchip contains unidirectionally oriented fibers and a cured resin.

Each of the additional scarf plug layers 50 a-50 i has an interior sideand an exterior side. For example the interior side of additional scarfplug layer 50 a is shown at 52 and the exterior side is shown at 54. Theadditional scarf plug layers 50 a-50 i are located in the scarf plug 42such that the interior side of each additional scarf plug layer islocated next to the exterior side of an adjacent additional scarf pluglayer that is closer to the first scarf plug layer 44. The interior sideof additional scarf plug layer 50 a is located next to the exterior side48 of the first scarf plug layer and follows the surface contour 48 ofthe first scarf plug layer. The additional scarf plug layers 50 a-50 iterminate at and/or form the seam boundary 40 that is coincident withthe tooling seam surface.

The angle 60 between the first scarf surface 20 and the seam boundary 40(also referred to as the chamfer) should be between 20 and 45 degrees.The chamfer or angle 62 between the second scarf surface 30 and the seamboundary 40 should also be between 20 and 45 degrees. It was discoveredthat the angle of the chevron shape for the scarf plug was important inproviding an adequate seam having low levels of porosity. Scarf plugsfilling seams with chamfers of over 45 degrees are not suitable.Chamfers of between 45 and 35 degrees provide seams that are acceptablefor many molding applications. However, for tooling that will be used inautoclaves at high temperatures and high pressures, it is preferred thatthe chamfer be between 25 and 35 degrees. Seams with chamfers of 30degrees were found to provide particularly effective seams that are notporous and which are particularly suitable for use in tooling that isexposed to the high pressures and temperatures that occur duringautoclave molding of composite parts.

A side sectional view of a chevron-shaped scarf plug is shown in FIG. 6where the scarf plug is in place within a seam that is bordered on eachside by a composite tooling made with multiple layers of 4000 grams persquare meter (gsm) M61 HexTool® sheet molding compound. The scarf plugwas made from 10 layers of 4000 grams per square meter (gsm) M61HexTool® sheet molding compound. The chamfer for the first and secondtooling sections in FIG. 6 is 45 degrees. The top of the scarf plug,which forms the exterior boundary 40, is 5 cm wide.

A side sectional view of chevron-shaped scarf plug in place in a seamthat is bordered on each side by composite tooling made with multiplelayers of 4000 grams per square meter (gsm) M61 HexTool® sheet moldingcompound is also shown in FIG. 7. The scarf plug was made from 10 layersof 4000 grams per square meter (gsm) M61 HexTool® sheet moldingcompound. In FIG. 7, the chamfer for the first and second toolingsections is 30 degrees. The top of the scarf plug is also 5 cm wide. Thetop of the scarf plugs are typically from 2 to 10 cm wide.

The scarf plugs and tooling sections shown in FIGS. 6 and 7 were bothprepared in the same manner following standard procedures for moldingM61 HexTool® sheet molding compound. It was discovered that the 30degree scarf plug shown in FIG. 7 had interlaminar porosity and bondlineporosity that was substantially less than the 45 degree scarf plug shownin FIG. 6. Accordingly, the scarf plug design shown is FIG. 7 ispreferred for seaming multi-sectional tooling that will be used inautoclaves that operate at temperatures above 150° C. and pressures of45 psi to 125 psi.

It is preferred that a layer of scarf plug adhesive be located betweenthe scarf plug 42 and the first and second scarf surfaces 20 and 30, asshown at 70 and 72, respectively. The material used as the scarf plugadhesive can be any suitable adhesive that is compatible with the resinused in the scarf plug and tooling sections. For high temperaturemolding (150° C. and above), adhesives made from bismaleimide,polyimide, polyether ether ketone, phenolic and the like are preferred.HP655 bismaleimide film adhesive, which is available from HexcelCorporation (Salt Lake City, Utah), is a preferred scarf plug adhesive.The adhesive layer is preferably as thin as possible while stillproviding desired levels of bonding. Preferred thicknesses for theadhesive layer range from 20 microns to 1.5 mm thick.

The space or gap between side surfaces 18 and 28 is sealed with a layerof sealant or adhesive 80. The material used as the sealant can be anysuitable sealant or adhesive that is compatible with the resin used inthe tooling sections. For high temperature molding (150° C. and above),sealants made from bismaleimide, polyimide, polyether ether ketone,phenolic and the like are preferred. HP655 bismaleimide film adhesive isa preferred sealant. The gap 36 is preferably from 1 mm to 4 mm wide.

The scarf seam 36 is initially over filled with a consolidated scarfplug that is composed of uncured layers of quasi-isotropic sheet moldingcompound that have been consolidated under pressure and elevatedtemperature to form a chevron-shaped plug that closely matches the shapeof the scarf seam 36. The consolidated scarf plug is slightly largerthan the scarf seam so that when the consolidated scarf plug is cured,it forms an over-sized scarf plug as shown at 90 in FIG. 3.

It should be noted that the gap between side surfaces 18 and 28 issealed with sealant layer 80 prior to the consolidated scarf plug beingplaced into the scarf seam 36. The pre-positioning of the sealant layer80 is required in order to provide a seal between the tooling sections12 and 14 so that pressure can be applied during molding of theconsolidated scarf plug to form the cured over-sized scarf plug 90.

The portion 92 of the over-sized cured scarf plug 90, which is locatedabove the exterior boundary of the seam (shown in phantom at 40 in FIG.3), is removed to provide a scarf plug having a scarf surface thatcoincides with the exterior seam boundary 40. The excess portion of theover-sized scarf plug is removed using any of the known machining toolsand techniques that are commonly used in machining steel and/orcomposite material molds. Such machining tools typically employ carbideand diamond coated numerical controlled (N/C) cutters. The scarf plugsurface and surrounding tooling surfaces are machined and polished, ifnecessary, to achieve desired surface tolerances. Typical surfacetolerances are on the order of ±0.2 mm or less. The tooling surface andseam surface tolerances can be on the order of ±0.1 mm and even asaccurate as ±100 microns.

Since the scarf plug 42 and surrounding tooling surfaces are made fromthe same type of quasi-isotropic sheet molding compound, the machiningand polishing of these surfaces produces a multi-sectional toolingsurface that is virtually seamless. Another advantage is that the scarfplug surface has the same durability as the tooling surface when thetooling is used repeatedly to autoclave mold composite parts at hightemperatures and high pressures. Further, the tendency for cracks toform along the bond lines between the scarf plug and tooling sections isreduced because both the scarf plug and tooling sections have the samecoefficient of thermal expansion. In addition, the scarf plug can bemachined and polished in the same manner as the tooling sections whenthe tooling surface requires reconditioning or modification.

A consolidated scarf plug that is used to over-fill seam 36 is shown at100 in FIG. 4. The consolidated scarf plug 100 includes a firstconsolidated scarf plug layer 150 which corresponds to the first scarfplug layer 50 shown in FIG. 2. The consolidated scarf plug 100 alsoincludes additional consolidated scarf plug layers 150 a-150 i, whichcorrespond to additional scarf plug layers 50 a-50 i shown in FIG. 2.The consolidated scarf plug 100 is shown having an additional layer 150j.

The exterior side of the first consolidated scarf plug layer 150 is inthe shape of a chevron having an interior angle 152. In order to fitinto the seam formed by the first and second tool sections, which arechamfered at 20 to 45 degrees, the interior angle of the scarf chevroncan range from 90 to 140 degrees. Preferably the interior angle of thechevron will be from 110 to 130 degrees in order to match tooling seamchamfers of 25-35 degrees. The preferred interior angle of the chevronis 120 degrees which corresponds to the preferred tooling seam chamferof 30 degrees.

The consolidated scarf plug 150 is made by placing suitably sized layersof quasi-isotropic sheet molding compound in a consolidation mold, suchas the simplified compression mold shown at 110 in FIGS. 8 and 9. Themold 110 includes a mold body 111 and a removable top plate 112. Thebottom 113 of the top plate 112 and the inside surfaces 114 and 115 ofthe consolidation mold 111 are shaped to provide a chevron-shaped moldcavity 116 that closely matches the desired scarf plug shape which inturn closely matches the shape of the seam being filled. The mold issized so that the top 154 of the consolidated scarf plug over fills theseam, as described previously. The number of layers of quasi-isotropicsheet molding compound that are used for a particular scarf plug willtypically vary from 5 to 30 depending upon the thickness of the layersand the size of the scarf plug.

Once the layers of uncured quasi-isotropic sheet molding compound arelocated in the consolidation mold cavity 116, the top plate 112 issecured in place. The mold 110 is then pressurized by a forceapplication system, shown schematically at 117, and heated by a heatingsystem, shown schematically at 118, to consolidate the layers into asolid uncured laminate which forms the consolidated scarf plug. Theamount of heat and pressure that is applied to the layers ofquasi-isotropic sheet molding compound is sufficient to consolidate thelayers into a solid laminate without advancing the cure of the moldingcompound resin. It is desirable that curing of the molding compoundresin does not occur until the consolidated scarf plug is located in theseam between the tooling sections. For a quasi- isotropic sheet moldingcompound composed of carbon fibers and a bismaleimide resin, the typicalconsolidation process will take from 5 minutes to 30 minutes at atemperature of 60 to 95° C. with an applied force on the mold of 30,000to 50,000 pounds.

The consolidation mold 110 and the process for heating and pressurizingthe mold cavity 116 are particularly well suited for formingquasi-isotropic sheet molding compound into uncured consolidated scarfplug preforms. However, the mold and consolidation process may also beused to form a wide variety of other consolidated preform shapes fromquasi-isotropic sheet molding compound. The interior surfaces of themold and top plate can be modified and shaped as desired to form a widevariety of cavity shapes. The resulting mold can then be used to formconsolidated preforms which are curable to form a wide variety complexparts and structures including parts and structures used in aircraft andother aerospace vehicles.

Once formed, the consolidated scarf plug 150 may be used immediately orit can be stored under conditions that prevent curing of the uncuredresin present in the consolidated scarf plug. An advantage provided bythe consolidated scarf plug is that it can be manufactured and stored atone location and then shipped to another location where themulti-sectional tooling is being assembled. In addition, sets ofdifferent sized consolidated scarf plugs can be manufactured and storedin order to provide a ready supply of scarf plugs for sealing a varietyof seams in multi-sectional tooling located at various locations.

The consolidated scarf plug 150 may be made from any of thequasi-isotropic sheet molding compounds that have been used to makecomposite tooling. Sheet molding compound made from chips composed ofunidirectional carbon tows and a bismaleimide resin are preferred. Apreferred exemplary quasi-isotropic sheet molding compound is HexTool®M61. HexTool® M61 is available in areal weights of 2000 gsm and 4000gsm.The nominal chip size is 8 mm wide and 50 mm long. Each chip containscarbon fibers and 38 percent by weight bismaleimide resin. The thicknessof a cured layer of HexTool® M61 is 1.27 mm for the 2000 gsm sheetmolding compound and 2.54 mm for the 4000 gsm material. The Tg of postcured HexTool® M61 is 275° C. with the maximum use temperature being218° C. The coefficient of linear thermal expansion of cured HexTool®M61 is 4.0×10⁻⁶/° C. (in Plane ASTME 289-95).

The consolidated scarf plug and tooling sections may be made from thesame quasi-isotropic sheet molding compound or they can be made fromdifferent quasi-isotropic sheet molding compound. For example, 4000 gsmHexTool® M61 is commonly used to make composite tooling. The scarf plugcan also be made from 4000 gsm HexTool® M61 to match the toolingsections. In this case, from 8 to 12 layers of sheet molding compoundare used to make a scarf plug that has a top surface that isapproximately 5 cm wide.

Alternatively, 2000 gsm HexTool® M61 may be used to make scarf plugs forseaming together tooling sections made from 4000 gsm HexTool® M61. Thelower areal weight sheet molding compound is useful where higherflexibility for the consolidated scarf plug is desired. 2000 gsmHexTool® M61 is a preferred sheet molding compound because the resultingscarf plugs tend to have reduced amounts of wrinkles or folds. When 2000gsm HexTool® M61 is used to make scarf plugs, the number of layers ofsheet molding compound needed for a scarf plug having top surface thatis 5 cm wide will range from 16 to 24 layers.

A portion of an exemplary multi-sectional composite tooling is shown at200 in FIG. 5. The multi-sectional tooling 200 includes a first toolingsection 202, a second tooling section 204 and a third tooling section206. A first seam 208 is located between the first and second toolingsections 202 and 204. A second seam 210 is located between the first andthird tooling sections 202 and 206. A third seam 212 is located betweenthe second and third tooling sections 204 and 206. The three seams 208,210 and 212 are shown partially filled with scarf plugs 214, 216 and 218in accordance with the present invention. The three seams meet at aT-junction 220. The scarf plugs 216 and 218 may be a single scarf plug.The scarf plugs may be overlapped or butt-jointed at junction 220. Inaddition, the T-junction can be formed as a single T-shaped consolidatedscarf plug, if desired.

The three piece multi-sectional composite tooling is shown at 200 inFIG. 5 is an additional example of how multiple seams and a seamjunction can be filled with scarf plugs in accordance with the presentinvention. As was the case with the exemplary two piece tooling 10, itwill be recognized that the actual multi-sectional composite toolingwill typically be made up of numerous tooling sections that are seamedtogether with numerous scarf plugs.

Having thus described exemplary embodiments of the present invention, itshould be noted by those skilled in the art that the within disclosuresare exemplary only and that various other alternatives, adaptations andmodifications may be made within the scope of the present invention.Accordingly, the present invention is not limited to the above preferredembodiments and examples, but is only limited by the following claims.

What is claimed:
 1. A multi-sectional tooling for use in molding a largecomposite structure that has a molded surface, said multi-sectionaltooling comprising: a first tooling section comprising a first toolsurface which is shaped to form a first portion of the molded surface ofsaid large composite structure, a first side surface and a first scarfsurface extending at an angle from said first tooling surface to saidfirst side surface, said first scarf surface having a first exterioredge located at said first tooling surface and a first interior edgelocated at said first side surface, said first tooling sectioncomprising multiple layers of cured quasi-isotropic sheet moldingcompound, said layers of sheet molding compound each comprising aplurality of randomly oriented chips wherein said chips compriseunidirectionally oriented fibers and a cured resin; a second toolingsection comprising a second tooling surface which is shaped to form asecond portion of the molded surface of said large composite structure,a second side surface and a second scarf surface extending at an anglefrom said second tooling surface to said second side surface, saidsecond scarf surface having a second exterior edge located at saidsecond tooling surface and a second interior edge located at said secondside surface, said second tooling section comprising multiple layers ofcured quasi-isotropic sheet molding compound, said layers of sheetmolding compound each comprising a plurality of randomly oriented chipswherein said chips comprise unidirectionally oriented fibers and a curedresin, wherein said first tooling section and second tooling section arelocated adjacent to each other so that said first scarf surface and saidsecond scarf surface form a scarf seam between said first and secondtooling sections, said scarf seam having an apex extending along saidfirst and second interior edges and an exterior boundary extendingbetween said first and second exterior edges, said exterior boundarybeing coincident with a tooling seam surface extending between saidfirst tooling surface and second tooling surface; a sealant layerlocated between said first and second side surfaces, said sealant layerbeing located outside of said scarf seam; and a scarf plug that fillssaid scarf seam, said scarf plug comprising a first scarf plug layerwhich comprises a layer of cured quasi-isotropic sheet molding compoundcomprising a plurality of randomly oriented chips wherein said chipscomprise unidirectionally oriented fibers and a cured resin, said firstscarf plug layer having an interior side and an exterior side whereinthe interior side of said first scarf plug layer is located adjacent tosaid first and second scarf surfaces and extends from said firstexterior edge to said apex and from said apex to said second exterioredge and wherein said exterior side of said first scarf plug layer has asurface contour in the shape of a chevron extending from said firstexterior edge to said second exterior edge, said scarf plug comprising aplurality of additional scarf plug layers located between the exteriorside of said first scarf plug layer and the exterior boundary of saidscarf seam, each of said additional scarf plug layers comprising a layerof cured quasi-isotropic sheet molding compound comprising a pluralityof randomly oriented chips wherein said chips comprise unidirectionallyoriented fibers and a cured resin and wherein each of said additionalscarf plug layers has an interior side and an exterior side, saidadditional scarf plug layers being located in said scarf plug such thatthe interior side of each additional scarf plug layer is located next tothe exterior side of an adjacent additional scarf plug layer that iscloser to said first scarf plug layer and wherein the interior side ofone of said additional scarf plug layers is located next to the exteriorside of said first scarf plug layer and follows the surface contour ofsaid first scarf plug layer and wherein said additional scarf pluglayers form said tooling seam surface.
 2. A multi-sectional tooling foruse in molding a large composite structure according to claim 1 whereinthe angle between the first scarf surface and said exterior boundary isbetween 25 degrees and 35 degrees and wherein the angle between thesecond scarf surface and said exterior boundary is between 25 degreesand 35 degrees.
 3. A multi-sectional tooling for use in molding a largecomposite structure according to claim 2 wherein the angle between thefirst scarf surface and said exterior boundary is between 30 degrees andwherein the angle between the second scarf surface and said exteriorboundary is 30 degrees.
 4. A multi-sectional tooling for use in moldinga large composite structure according to claim 1 wherein the firsttooling section, second tooling section and scarf plug are made fromlayers of sheet molding compound having the same areal weight.
 5. Amulti-sectional tooling for use in molding a large composite structureaccording to claim 1 wherein the areal weight of the layers of sheetmolding compound used to make the first tooling section and secondtooling section have an areal weight that is greater than the arealweight of the layers of sheet molding compound used to make said scarfplug.
 6. A multi-sectional tooling for use in molding a large compositestructure according to claim 1 wherein the first tooling section, secondtooling section and scarf plug each comprises chips comprising carbonfibers and cured bismaleimide resin.
 7. A multi-sectional tooling foruse in molding a large composite structure according to claim 1 whereinthe exterior boundary of said scarf seam extending between said firstand second exterior edges is from 2 cm to 10 cm wide.
 8. Amulti-sectional tooling for use in molding a large composite structureaccording to claim 1 wherein a first layer of scarf plug adhesive islocated between said first scarf surface and the interior side of saidfirst scarf plug layer and a second layer of scarf plug adhesive islocated between said second scarf surface and the interior side of saidfirst scarf plug layer.
 9. A consolidated uncured scarf plug for use insealing a seam in a multi-sectional tooling which is used to mold largecomposite structures that have a molded surface, Wherein saidmulti-sectional tool has a first tooling section comprising a firsttooling surface which is shaped to form a first portion of the moldedsurface of the large composite structure, a first side surface and afirst scarf surface extending at an angle from the first tooling surfaceto the first side surface, the first scarf surface having a firstexterior edge located at the first tooling surface and a first interioredge located at the first side surface, the first tooling sectioncomprising multiple layers of cured quasi-isotropic sheet moldingcompound, the layers of sheet molding compound each comprising aplurality of randomly oriented chips wherein said chips compriseunidirectionally oriented fibers and a cured resin, said multi-sectionaltooling further including a second tooling section comprising a secondtooling surface which is shaped to form a second portion of the moldedsurface of the large composite structure, a second side surface and asecond scarf surface extending at an angle from the second toolingsurface to the second side surface, the second scarf surface having asecond exterior edge located at the second tooling surface and a secondinterior edge located at the second side surface, the second toolingsection comprising multiple layers of cured quasi-isotropic sheetmolding compound, the layers of sheet molding compound each comprising aplurality of randomly oriented chips wherein the chips compriseunidirectionally oriented fibers and a cured resin, wherein the firsttooling section and second tooling section are located adjacent to eachother so that said first scarf surface and the second scarf surface forma scarf seam between the first and second tooling sections, the scarfseam haying an apex extending along the first and second interior edges,the scarf seam having an exterior boundary extending between the firstand second exterior edges, wherein the consolidated uncured scarf plugis used to overfill the scarf seam, the consolidated uncured scarf plugcomprising: a first consolidated scarf plug layer which comprises alayer of consolidated quasi-isotropic sheet molding compound comprisinga plurality of randomly oriented chips wherein said chips compriseunidirectionally oriented fibers and an uncured resin, said firstconsolidated scarf plug layer having an interior side and an exteriorside wherein the interior side of said first consolidated scarf pluglayer is shaped to be located adjacent to the first and second scarfsurfaces and extend from the first exterior edge to the apex and fromthe apex to the second exterior edge and wherein said exterior side ofsaid first consolidated scarf plug layer has a surface contour extendingfrom said first exterior edge to said second exterior edge that is inthe shape of a chevron haying an interior angle, said consolidateduncured scarf plug comprising a plurality of additional consolidatedscarf plug layers located on the exterior side of said firstconsolidated scarf plug layer, each of said additional consolidatedscarf plug layers comprising a consolidated quasi-isotropic sheetmolding compound comprising a plurality of randomly oriented chipswherein said chips comprise unidirectionally oriented fibers and anuncured resin and wherein each of said additional consolidated scarfplug layers has an interior side and an exterior side, said additionalconsolidated scarf plug layers being located in said consolidateduncured scarf plug such that the interior side of each additionalconsolidated scarf plug layer is located next to the exterior side of anadjacent additional consolidated scarf plug layer that is closer to saidfirst consolidated scarf plug layer and wherein the interior side of oneof said additional consolidated scarf plug layers is located next to theexterior side of said consolidated first scarf plug layer and followsthe surface contour of said first consolidated scarf plug layer, saidadditional consolidated scarf plug layers being shaped to extend pastthe exterior boundary of the scarf seam and overfill said scarf seamwhen said consolidate uncured scarf plug is placed within said scarfseam.
 10. A consolidated uncured scarf plug according to claim 9 whereinthe interior angle of said chevron is between 110 degrees and 130degrees.
 11. A consolidated uncured scarf plug according to claim 10wherein the interior angle of said chevron is 120 degrees.
 12. Aconsolidated uncured scarf plug according to claim 9 wherein said firstconsolidated scarf plug layer and said additional consolidated scarfplug layers each comprises chips comprising carbon fibers and uncuredbismaleimide resin.
 13. A consolidated uncured scarf plug according toclaim 9 wherein the first consolidated scarf plug layer and additionalconsolidated scarf plug layers are sized and shaped to over fill a scarfseam where the exterior boundary of the scarf seam is from 2 cm to 10 cmwide.
 14. A consolidated uncured scarf plug according to claim 9 whereinthe first consolidated scarf plug layer and said additional scarf pluglayers are made from layers of consolidated quasi-isotropic sheetmolding compound having the same areal weight.
 15. A method for seaminga multi-sectional tooling that is used in molding a large compositestructure that has a molded surface, said method comprising the stepsof: providing a first tooling section comprising a first tooling surfacewhich is shaped to form a first portion of the molded surface of saidlarge composite structure, a first side surface and a first scarfsurface extending at an angle from said first tooling surface to saidfirst side surface, said first scarf surface having a first exterioredge located at said first tooling surface and a first interior edgelocated at said first side surface, said first tooling sectioncomprising multiple layers of cured quasi-isotropic sheet moldingcompound, said layers of sheet molding compound each comprising aplurality of randomly oriented chips wherein said chips compriseunidirectionally oriented fibers and a cured resin; providing a secondtooling section comprising a second tooling surface which is shaped toform a second portion of the molded surface of said large compositestructure, a second side surface and a second scarf surface extending atan angle from said second tooling surface to said second side surface,said second scarf surface having a second exterior edge located at saidsecond tooling surface and a second interior edge located at said secondside surface, said second tooling section comprising multiple layers ofcured quasi-isotropic sheet molding compound, said layers of sheetmolding compound each comprising a plurality of randomly oriented chips.wherein said chips comprise unidirectionally oriented fibers and a curedresin; locating said first tooling section and second tooling sectionadjacent to each other so that said first scarf surface and said secondscarf surface form a scarf seam between said first and second toolingsections, said scarf seam having an apex extending along said first andsecond interior edges and an exterior boundary extending between saidfirst and second exterior edges; placing a layer of sealant layerbetween said first and second side surfaces, said sealant layer beinglocated outside of said scarf semi, and overfilling said scarf seam witha consolidated uncured scarf plug which comprises a first consolidatedscarf plug layer that is composed of a layer of consolidatedquasi-isotropic sheet molding compound comprising a plurality ofrandomly oriented chips wherein said chips comprise unidirectionallyoriented fibers and an uncured resin, said first consolidated scarf pluglayer haying an interior side and an exterior side wherein the interiorside of said first consolidated scarf plug layer is located adjacent tothe first and second scarf surfaces and extends from the first exterioredge to the apex and from the apex to the second exterior edge andwherein said exterior side of said first consolidated scarf plug layerhas a surface contour extending from said first exterior edge to saidsecond exterior edge that is in the shape of a chevron having aninterior angle that is the same as the angle between the first scarfsurface and the second scarf surface at the apex of said scarf seam saidconsolidated scarf plug comprising a plurality of additionalconsolidated scarf plug layers located on the exterior side of saidfirst consolidated scarf plug layer, each of said additionalconsolidated scarf plug layers comprising a consolidated quasi-isotropicsheet molding compound comprising a plurality of randomly oriented chipswherein said chips comprise unidirectionally oriented fibers and anuncured resin and wherein each of said additional consolidated scarfplug layers has an interior side and an exterior side, said additionalconsolidated scarf plug layers being located in said consolidated scarfplug such that the interior side of each additional consolidated scarfplug layer is located next to the exterior side of an adjacentadditional consolidated scarf plug layer that is closer to said firstconsolidated scarf plug layer and wherein the interior side of one ofsaid additional consolidated scarf plug layers is located adjacent tothe exterior side of said first consolidated scarf plug layer andfollows the surface contour of said consolidated first scarf plug layer,wherein one or more of said additional consolidated scarf plug layersextend past the exterior boundary of the scarf seam in order to overfillsaid scarf seam; curing said consolidated uncured scarf plug that hasoverfilled said scarf seam to form a cured oversized scarf plug whichincludes a portion that extends past the exterior boundary of the scarfseam; and removing the portion of said cured oversized scarf plug thatextends past the exterior boundary of the scarf seam to thereby form atooling seam surface that extends between said first tooling surface andsaid second tooling surface.
 16. A method for seaming a multi-sectionaltooling according to claim 15 wherein the angle between the first scarfsurface and said exterior boundary is between 25 degrees and 35 degreesand wherein the angle between the second scarf surface and said exteriorboundary is between 25 degrees and 35 degrees.
 17. A method for seaminga multi-sectional tooling according to claim 16 wherein the anglebetween the first scarf surface and said exterior boundary is between 30degrees and wherein the angle between the second scarf surface and saidexterior boundary is 30 degrees.
 18. A method for seaming amulti-sectional tooling according to claim 15 which includes theadditional steps of locating a first layer of scarf plug adhesivebetween said first scarf surface and the interior side of said firstscarf plug layer and locating a second layer of scarf plug adhesivebetween said second scarf surface and the interior side of said firstscarf plug layer.
 19. A method for seaming a multi-sectional toolingaccording to claim 15 wherein the areal weight of the layers of sheetmolding compound used to make the first tooling section and secondtooling section have an areal weight that is greater than the arealweight of the layers of consolidated quasi-isotropic sheet moldingcompound used to make said consolidated uncured scarf plug.
 20. A methodfor seaming a multi-sectional tooling according to claim 13 wherein thefirst tooling section and second tooling section each comprises chipscomprising carbon fibers and cured bismaleimide resin and saidconsolidated uncured scarf plug comprises carbon fibers and uncuredbismaleimide resin.